Voltage regulation



Patented May 31, 1949 UNITED STATES were PATENT OFFICE 2.41am vouracaroom-non Application April is, ms, Serial No. team 8 Claims. (Cl.175-388) This invention relates to voltage regulation and particularlyto a regulated rectifier for supplying rectified current to a load.

An object of the invention is to provide an improved regulated rectifierfor supplying rectified current to a load while minimizing load voltagevariations.

In a specific embodiment of the invention herein shown and described forthe purpose of illustration. there is provided a rectifier employingthree electrode space discharge rectifying tubes, preferably of thegas-filled type. for supplying current to a load through aninductance-capacity filter and through a series load compoundingresistor one terminal of which is connected to the negative loadterminal. The load current may have an average value which varies over aconsiderable range and also large amplitude changes of signalingfrequencies. A shunt current path connected across the load comprises inseries a resistor and the space current path of a space current deviceor shunt regulator tube. There is impressed upon a circuit connectingthe con-' trol electrode and cathode of the shunt-regulator tube acontrol voltage having three component voltages for controlling thespace current in the shunt regulator tube and thereby the voltage dropin the circuit for supplying the rectified current to the load includingthe drop across the load compounding resistor. One of the componentvoltages is the voltage drop across the load compounding resistor. Asthe load increases, for example, the voltage drop across the loadcompounding resistor increases to make the potential of the controlelectrode of the'shunt regulator tube relatively more negative withrespect to the cathode potential to cause a reduction of the spacecurrent in the shunt regulator tube and,-

therefore, to cause the current supplied to the load to increase,thereby tending to prevent a reduction of load voltage due to theincrease in load. A second of the component voltages is obtained from anauxiliary rectifier for rectifying current from the alternating currentsupply source to produce an output voltage which varies inversely wtihline voltage. When the line voltage increases, for example, the secondcomponent voltage makes the control electrode of the shunt regulatortube relatively less negative with respect to the cathode potential tocause the shunt regulator tube to draw more space current, thusminimizing or substantially preventing an increase of current suppliedto the load due to the rise of line voltage and thus tending to preventan increase of load voltage.

2 The regulated rectifier may be used to supp y current to telegraph orother signaling apparatus such that the load current may have largeamplitude variations occurring at signaling frequencies in addition tolarge changes of average current. Load voltage variations due to loadchanges at relatively high frequencies are effectively suppressed by theinductance-capacity filter. At lower frequencies load compensation isprovided by the action of the shunt regulator tube and the regulatingvoltage component across the load compounding resistor. It was founddesirable, however, to provide additional compensation to reduce oreliminate voltage variations within the frequency range from about fivecycles to several hundred cycles. Load voltage variations within afrequency rang for which additional compensation is desired are,therefore, im-

pressed as the third regulating voltage component upon the controlelectrode-cathode circuit of the shunt regulating tube. Within thisfrequency range an increase of load voltage makes the control grid ofthe shunt regulating tube relatively more positive to cause the spacecurrent in the tube to increase and the load current to decrease thustending to prevent the rise of load voltage. Load voltage variationswithin this frequency range are thus effectively reduced.

There is provided a circuit for controlling the potential of the controlelectrode with respect to the cathode potential of each of the spacedischarge rectifier tubes. For normal operation oi. the regulatedrectifier there is impressed upon the control electrode-cathode circuitsof the rectifier tubes a voltage which varies in accordance with changesof average space current in the shunt regulator tube. The average spacecurrent of the shunt regulator tube is thus maintained within suchlimits of its operating range that large transient changes of spacecurrent may" take place within the operating limits of a particulartube. when the rectifier circuit is started in operation, or when poweris restored following a power interruption, the control circuitfunctions to apply an exponentially decreasing negativebiasing-potential to the control electrodes of the rectifier tubesthereby preventing the flow of space current in the rectifier tubeswhile the cathodes are being heated to operating temperature and, thus,preventing damaging the cathodes. For setting up the exponentiallychanging biasing voltage there is provided an auxiliary rectifier and acondenser in series in the control electrode-cathode circuit of thespace discharge tubes of the main rectifier and a high time constantcharging circuit for the condenser including the relatively high reverseresistance of an asymmetrically conducting element or varistor oi thecopper oxide type. When the rectifier tubes 'are conducting, thecondenser may discharge under control of the shunt regulating tubecircuit at arelatively rapid rate through a circuit including therelatively low forward resistance of the varistor, current flowingthrough a circuit including the anode-control grid paths of therectifier tubes and through the relatively low for-- ward resistance ofthe varistor.

The single figure of the drawing is a schematic view of a regulatedrectifier embodying the inven- There is provided a transformer havin aprimary winding I 6 to which alternating cur- I rent from'a source i1 issupplied when switch i8 is closed and having secondary windings 2i, 22.23 and 24. Winding 2i supplies heating current to the cathodes of tubesI 0 and ii. a mid-tap of the winding and the cathodes being connected tothe positive load terminal. One end terminal of winding 22 is connectedthrough an inductance element 25 to the anode of tube l0 and the otherend terminal of winding 22 is connected through an inductance element 26to the anode of tube ii. A mid-terminal of winding 22 is connectedthrough an inductance element i 3 and through resistor i5 to thenegative load terminal. microfar'ad condenser 21 is connected acrosssecondary winding 22. Condensers 28 and 29, each of 0.01 microfarad, areconnected in series across the winding 22, a common terminal of thecondenser being connected to the mid-tap of winding 21 and to the tubecathodes.

A shunt regulator tube 30 which may be of the RCA 6Y6 type has its spacecurrent path confrom transformer winding 24. There is provided a currentath comprising in series an auxiliary rectifier 33 of ,the'varistorbridge type, the positive output terminal of which is connected to thepositive lo'ad terminaL-a 4-microfarad condenser 34 and a 4-microfaradcondenser 35, one terminal of which is connected to the common terminalof inductance element i3 and of resistor 15. "A common terminal ofcondensers 34 and 35 is connected to the control gridof tube i 0 through22,000- -ohm resistor 36 and to the control grid of tube ii through22.000-ohm resistor 31. The

common terminal of condensers 34 and 35 is connected through anasymmetrically conducting element or varistor 38 of the copper oxidetype. shunted by a 3-megohm resistor 39 and a 15,000- ohm resistor 40 inseries therewith to the anode of tube 30. Varistors are described in anarticle ing in a circuit whichmay be traced from the by J. A. Becker onpage 322 et seq. of Bell Laboratories Record" for July 1940. The commonterminal of varistor 33. resistor 33 and resistor 40 is connectedthrough a d-microfarad condenser to the positive load terminal. There isconnected across the load a current path comprising in series a4-microfarad condenser 42. one terminal of which is connected to thepositive load terminal and the primary winding 43 of a transformerhaving a secondary winding 44. the transformer having a voltage step-upratio to give a secondary voltage of 10 to times the primary voltage.One terminal of the winding 44 is connected through a 100,000-ohmresistor 45 .to the control grid tube 33. the common terminal of winding44 and resistor 45 being connected through a condenser 43 to the cathodeof tube 30.

A circuit connecting the control electrode and cathode of tube 30 may betraced from the control electrode through resistor 45, transformerwinding 44, resistor 41 of 100.000 ohms and through load compoundingresistor i5 to the cathode. A unidirectional voltage which variesinversely with the voltage of source i1 is set up across the resistor 41by a circuit arrangement described as follows:

The end terminals of transformer winding 23. across which anelectromotive force of about 345 volts appears, are connected to acircuit comprising in series a thermistor 50, an ambient temperaturecompensating resistor 5| and a 12,000- ohm resistor 52. A thermistor isa resistance element made from a class of materials known assemi-conductors which have a large negative temperature coefllcient ofresistance. Thermistors are described in an article by G. L. Pearson in"Bell Laboratories Record" for December 1940, page 106 et seq. A5,000-ohm potentiometer 55 is connected across a portion of transformerwinding 23 across which an electromotive force of about 1'7 volts is setup. The electromotive force appearing across the portion of transformerwinding 23 which connects a terminal of thermistor 50 with an endterminal of potentiometer 55 is about 20 volts. The adJustable tap ofpotentiometer 55 is connected to one plate of a 0.5-microfarad condenser53. The other plate of condenser 53 is connected through an asymmetricalvaristor or rectifying element 54 to a common terminal of resistors 5iand 52. The condenser 53 is shunted by a path comprising in seriesresistor 41 and a 47,000-ohm resistor 43. The condenser is 'thus chargedby current flowvariable tap of, potentiometer 52 to the positivelycharged plate of condenser 53 and from the negatively charged condenserplate through varistor 54 and resistor 52 to an end'terminal oftransformer 23. If the line voltage increases, for example, the currentthrough the circuit, comprising thermistor 50 and resistors 51 and 52 inseries. increases to cause the resistance of thermistor 50 to decrease.As a result the voltage across resistor 52 increases by a greaterpercentage than the percentage increase of the voltage acrosstransformer winding 23.- The voltage available for charging condenser 53is thus reduced with the result that the voltage to which the condenseris charged and the voltage drop across resistor 41 each decreases. Whenthe voltage of the supply source increases, for example, the rate ofdecrease of voltage across resistor 41 is greater than the rate ofincrease of the supply voltage.

It will be apparent, therefore, that when the line voltage increases,for example, with the resuit that the voltage drop across resistor 41decreases. the control grid of tube 8| will become relatively lessnegative with respect to the cathode potential to cause the spacecurrent in tube II to increase, thus tending to prevent an increase oicurrentilowing through the load It.

An increase of load voltage due to the increased line voltage is thusminimized or substantially prevented. So also, if the load is increased.the voltage drop across resistor II increases to make the control gridof shunt regulator tube more negative with respect to its cathode.thereby reducing the space current in the tube and causing the currentthrough the load to increase. The reduction of load voltage due to theincrease of load is thus minimized or substantially prevented.

Load voltage compensation is provided not only for average changes ofload but also for load changes occurring at signaling frequencies suchas those due to the production of telegraph signals and audio frequencysignals present in the load. The time constant of the circuit includingfilter condenser i4 and the load is suificiently large that the loadvoltage does not change to any appreciable extent over the short periodoi a wave of a relatively high frequency. At lower frequencies, when theload is decreased, for example. to make the control grid of tube 3| lessnegative due to the decreased voltage drop across resistor ll, the spacecurrent in tube II increases to cause a reduction of current through theload. This action, therefore, tends to prevent a rise of load voltagedue to the decrease in load. It was found, however, that additionalcompensation was required to reduce load voltage variations over afrequency range from about five to several hundred cycles. For thispurpose alternating components of the load voltage are impressed uponthe control grid-cathode circuit of shunt regulator tube II through acoupling circuit comprising condenser 42, transformer 43, I4 andcondenser 48. Within the specified frequency range, when the loadvoltage is increased, there is induced in winding ll of the transformera voltage of such polarity as to make the grid of the shunt regulatortube relatively less negative with respect to the cathode, therebycausing the space current in tube 30 to increase and the voltage dropacross resistor l5 and other resistance in series with the load toincrease. Changes of load voltage are thus minimized. The condenser I6is provided for causing 120-cycle feedback voltage components to beattenuated more than the lower frequency components, say in the range of5 to 50 cycles, thus making the circuit less effective insuppressing'the 120-cycle ripple frequency. This is done because in aparticular use of the circuit the 120-cycle load voltage variations werelarger than other frequency components so that the tube 30 would beoverloaded by the 120- cycle component if it were not first reduced inamplitude. A shunt regulator tube of larger capacity than the tube 30could of course be used in which case the condenser 46 could be omitted.However, in the application of the invention for which the circuit wasparticularly designed the suppression of the 120-cycle voltage componentwas found to be less important an the voltage regulation in thefrequency rang from 0 to 50 or 60 cycles.

In starting the operation of the regulated rectifying circuit inresponse to closure of switch l8 heating current is supplied to thecathodes of tubes l0 and II from transformer winding 2i, heating currentis supplied to the cathode heater of tube 30 from transformer winding24, current is supplied to the circuit connected to winding 28 andcurrent is supplied from winding 20 to auxiliary rectifier 88. In orderto avoid damaging the cathodes of tubes II and II while the cathodes arebeing heated to operating temperature. there is impressed upon thecontrol electrodes with respect to the cathodes a negative biasingpotential for preventing the flow of space current in the tubes, thisbiasing potential decreasing exponentially until a potential is reachedat which conduction in tubes "and ii is initiated. The action of thecircuit arrangement for setting up this biasing potential will now bedescribed.

When current is first supplied to the auxiliary rectifier 38 the controlgridsoi tubes I II and ii are-made about 30 volts negative due to theoutput voltage of rectifier 33. Current from this auxiliary rectifierquickly charges condensers H. II and 34 in series at which time thenegative biasing voltage is 15 volts, that is, the output voltage ofauxiliary rectifier 33 minus the voltage to which the condenser 34 ischarged. Con

denser continues to charge but at a relatively slow rate through acircuit comprising in series rectifier 33, condenser ll, the relativelyhigh reverse resistance or varistor 38, shunted by resistor 29, andcondenser 34. While condenser 34 is being charged, condenser 35discharges through condensers l4 and H and varistor 38 shunted byresistor 39. When the biasing voltage has decreased suiiiciently, tubesill and H become conducting, respectively, during alternate hall cyclesof the current from source i1. Rectified current is thus applied to theload circuit to set up a voltage across condenser II and across theload. The polarity of the voltage across condenser 35 now reverses, thiscondenser being charged by grid current, that is, current flowing in acircuit including the space between the anode and control grid of therectifier tube which is conducting, resistor 36 or resistor 31,condenser 35, a portion of transformer winding 22 and inductance element25 or 26. Grid current may also flow through a circuit comprisingcondenser 34, auxiliary rectifier 33 and condenser it to further chargecondenser 34 to cause the voltage in the control grid-cathode circuitsof tubes l0 and Ii to change in a direction such as to cause the tubesto start conducting earlier in each positive half-cycle of the anodevoltage and thus cause the load voltage to gradually increase. Due tothe voltage to which condenser 35 is charged by rid current of tubes i0and ii, current fiows in a shunt path across condenser 35 comprisin inseries varistor 38, resistor 40, the space current path of tube 30 andresistor l5. At this time,

therefore, the varistor 38 has a relatively low resistance so that thesmall voltage drop across the varistor has a negligibleefiect upon thecontrol electrodecathode circuit of tubes l0 and Ii.

It is desired to limit the changes of average space current in shuntregulator tube 30 so that large amplitude, short duration increases ordecreases of space current may take place for cf,- fecting regulation ofthe load voltage. The average voltage across resistor 3i is, therefore,impressed upon the control grid-cathode circuits of tubes l0 and i i,alternating components of the voltage drop across resistor 3| beingattenuated by the filtering action of resistor 40 and condenser Oneterminal of condenser 4! is connected to the cathodes of tubes Ill and Hand its other terminal is connected through the relatively low forwardresistance of varistor 38 and thrilugh resistor 36 to the control gridof tube Ill 7 and through resistor 81 to the control grid of tube ll. Asexplained above, it the load is decreased or ii the line voltageincreases the load voltage tends to rise. but this rise in load voltageis minimized or substantially prevented by causing the control electrodeof tube SI to be made relatively less negative with respect to thecathode and thus-causing the space current in tube 20 to rise. Anincrease in average space current The circuit is-so designed. that thespace current in shunt regulator tube 30 'may'vary above or 3 [anincreasingload voltage causing the current in below either of theselimiting values ofaverage space current by a. sufficient amplitude tocause current device having a. control means upon which a controlvoltage may be impressed (or controlling the space current in saiddevice, a resistor in series in said circuit through which now the loadcurrent and the current in said wshunt path, and means for setting up acontrol voltage having a plurality of components for controlling thecurrent in said space current device to minimize voltage changes acrosssaid load, said last-mentioned means comprising said resistor acrosswhich a first of said component voltages is set up, means energized bycurrent from said supply source for setting up a second componentvoltage, said second component voltage being a unidirectional voltagewhich decreases in re sponse to an increase of supply voltage and viceversa, and means for deriving an alternating voltage from saidloadvoltage to set up said third control voltage component, an. increase. oisaid first component voltage or of said second component voltage causingthe current in said space current device to decrease and vice versa, andan load voltage changes due to relatively brief fiuctuations'in linevoltage and load to be mini- -mized. It should be noted that as'soonasthe creased. thereby making the control grids or rectiller tubes Iii andii relatively more negative with respect to the cathodes and thusbringing the rectifier output voltage across condenser it back to itsprevious value. A hunting action which might otherwise take placedue-tothe delay in the application of a voltage change oc curring acrossresistor 3! to the controlelec-Z trode-cathode circuits of rectifiertubes i0 and ii is thus avoided.

, What is claimed is:

increase of said third component voltage due to said space currentdevice to increase.

I 3. Incornbination. means for rectifying current i from an alternatingcurrent supply source and for supplying the rectified current to aloadv 1. A rectifier for supplying rectifiedcurrentto a load comprislnga. space discharge device have ing an anode, a cathode and a controlelectrode,

a first circuit connecting, said anode and said-- cathode including asource of alternating current and said load, a shunt path across whichthe outing an initial period while the cathode of said device isbeingheated to operatingfteinperature and for causing space current toflow-through said device to said load subsequent to said initial througha circuit comprising "a resistor in series with the load,'one terminaloi.' said resistor being connected to the negativeload terminal, a spacedischarge device having an anode, a cathode and a control electrode,means for connecting said cathode to the negative load terminal, meansfor connecting said anode-to the positive load terminal, atransiormerlhavinga primary and t a secondary winding, a current pathconnected across said load comprising said primary transformer winding,a circuit connecting saidcontrol electrode and said cathode comprisingin series said secondary transiormerwinding and said re-,- sistor, meansenergized by current fromsaid alternating current source for setting upa, unidirectional voltage having variations corresponding to supplyvoltage variations, and-means for impressing said voltage upon saidcontrol electrode-cathode circuit.

period, and means efl'ective subsequent to said initial period forcausing the charge on said condenserto change for controlling thepotentialof ing current from an alternating current supply source and acircuit for supplying said rectified current to the load of a shuntcurrent path connected across said load comprising the space cursaidcontrol electrode withrespect to the potentialof said cathode, saidmeans comprisina means having a time constant which is low-with 1;.respect tothe time constant of said means for charging said condenserduring said initial -period'. v 2. The combination with a rectifier forrectify 4. Means for voltage variations across a load to which directcurrent is supplied from a rectifier of current from analternating;

current supply source, a first resistor in series with suppliedrtosaidload, one terminal of said first 'reslstorbeingconnected'to the negativeterminal of said load,-a flrst shunt. current path across saidload-comprising a'space current device having an "f 1 anode,'a'cathodeand a control electrode, said ,cathodebeihg connected to said negativeload terminal; meansenerglzed by current from ,.said-,

. alternating current supply source 'forfsettingnp "across-a secondresistor a unidirectional voltage a which decreases in response to avoltage increase .aoi' said supply source and vice versa, a transform.-

er havingaprima'ry and a secondary winding, a

second shunt current path connectedacross said load comprising theprimary windingoi said transformer, and a, clrcuit'connecting saidcontrol electrode andsaid cathode of said space current devicecomprising in series said first and secvond resistors and the secondarywinding of said transformer, the unidirectional voltages across saidfirst andsecond resistors being in aiding relationship and of suchpolarity as to make the potentialv of the control electrode negativewith respect to the cathode potential, the phase. of the alternatingvoltage set up across said secondary transformer winding being such asto make the control electrode relatively less negative with respect tothe cathode potential when the load voltage is increasing, and viceversa.

5. In combination, a space current device having an anode, a cathode anda control electrode, means for supplying space current to said devicefrom an alternating current supply source when said device isconducting, means for supplying heating current to said cathode fromsaid supply source, a rectifier to which the supply of energizingcurrent from said supply source is initiated simultaneously with thestarting of the supply of heating current to said cathode, means forconnecting the positive output terminal of said rectifier to saidcathode, a condenser having one of its terminals connected to thenegative output terminal of said rectifier, means for connecting theother terminal of said condenser to said control electrode, anasymmetrically conducting device, anda charging circuit for saidcondenser comprising said asymmetrically conducting device, chargingcurrent for said condenser flowing through said asymmetricallyconducting device in its reverse or high resistance direction therebydelaying the starting of conduction of space current in said spacecurrent device during a period in which said condenser is being charged.

6. In combination, a main rectifier including a space current devicehaving an anode, a cathode and a control electrode for rectifyingcurrent from an alternating current supply source and for supplying therectified current to a load, a filter condenser in a first pathconnected across the output of said main rectifier, an auxiliaryrectifier energized by current from said alternating current supplysource, a second current path connected across the output terminals ofsaid main rectifier comprising in series said auxiliary rectifier and asecond and a'third condenser, the positive output terminal of saidauxiliary rectifier being connected to the cathode of said space currentdevice, means for connecting the common terminal or said second andthird condensers 10 to said control electrode to control the biasthereof with respect to the cathode potential, a shunt path connectedacross said load comprising in series a first resistor and the spacecurrent path of a second space current device, said second space currentdevice having an anode connected to a terminal of said resistor and acathode connected to the negative load terminaL/means for controllingthe impedance of said second space current device for regulating theload voltage, a current path connecting the anode of said second spacecurrent device and the common terminal of said second and thirdcondensers comprising in series a second resistor, one terminal of whichis connected to said anode and an asymmetrically conducting device, afourth condenser in a path connecting the positive load terminal and acommon terminal of said asymmetrically conducting device and said secondresistor, said second and fourth condensers being charged by currentfrom said auxiliary rectifier through a circuit including the reverse orrelatively high resistance of said asymmetrically conducting device toset up an exponentially changing voltage for biasing the controlelectrode with respect to the cathode of said first space current deviceto delay conduction therein, the control electrode-cathode potential ofsaid first space current device being controlled subsequent toinitiation of conduction therein in accordance with changes of averagespace current in said second space current device to limit the changesof average space current in said second space current device.

JAMES A. POTTER.

' REFERENCES orrEn The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

